This invention relates to gaskets for automotive engines and, more particularly, to sealing applications with limited available compression area and to applications with variable land area.
In a typical environment for a valve cover gasket according to the present invention, engine flanges are available between which a gasket is needed for sealing purposes. When a gasket is installed between the engine flanges, fasteners such as bolts are positioned in holes formed in the flanges and gasket and are torqued down to suitably compress the gasket between the flanges. A typical gasket may be provided with a rigid core, such as metal, within a rubber or other elastomeric envelope, and with an elastomeric bead for sealing. Sometimes the bolts are excessively tightened to such an extent that the elastomer splits. This can cause fluid leakage and gasket failure.
In gaskets of this type, it has been determined that the splitting of the rubber is generally in line with the edge of the metal cores. It appears that when the gasket is compressed between the engine flanges, the rubber is excessively stressed in multiple directions and becomes displaced. When it is displaced along or towards the edge of a metal core, the core edge may cut the rubber which moves relative to it. The problem of splitting the rubber is of particular concern around the bolt holes. In the past, stops of hard, rigid material have been provided around the holes. For example, in U.S. Pat. No. 4,535,996, round, washer-like stops or limiters are provided which extend through holes in both the metal core and rubber envelope. These stops surround the bolt hole and, due to their rigidity, limit and restrict the deformation and displacement of the rubber in the zones around the bolt holes. The rubber is thus prevented from moving sufficiently to be cut by the edge of the metal core because when the stop engages the surfaces to be sealed, i.e., the engine flanges, it thereafter prevents further displacement of the rubber. Some engines have flanges with limited surface land area. When conventional compression limiters or stops are used in such applications, they may not seat on the contact surfaces and the stops therefore may not limit the bolt tightening, leading to split rubber and gasket failure. In addition, for those engines with limited land area at least in some areas of the flanges, the gasket must be constructed with a correspondingly limited dimension in those areas. If such a gasket were constructed with conventional round, washerlike stops, there would be insufficient space on the gasket to form a useful sealing bead because the stop might extend across substantially the entire width of the gasket. Thus, there is a need for a valve cover gasket assembly suitable for use in applications where the available flange width is very narrow.